Glenn J. Hoffman

Evapotranspiration of Mature Orange Trees Under Drip Irrigation in an Arid Climate

ABSTRACT EVAPOTRANSPIRATION (ET) of mature Valencia orange trees (Citrus sinensis L.) was determined from a large field experiment in southwest Arizona. ET was calculated as the difference between accurate measure-ments of the amount of water applied (rainfall included) and drainage below the root zone. The amount of drain-age was estimated from various techniques of calculating leaching fraction based on the ratios of total salt and chloride concentrations. In a climate where the annual pan evaporation is 2520 mm, ET was 1470 mm or about 50 m3 per tree. The daily rate of ET, averaged by month, ranged from a low of 0.8 mm in December to 7.5 mm in August. Sev-eral predictive equations for ET were in close agreement with these values.

Trickle irrigation rates and soil salinity distribution in an almond (Prunus amygdalus) orchard

Abstract Managing the soluble salts in the root zone of a trickle irrigated almond (Prunus amygdalus) orchard is desirable for tree growth and nut production. This study was conducted to determine the relationships among the volume (50, 100, and 150% of the crop evapotranspiration ( et c) of trickleapplied water and the amount and distribution of soil salinity, Cl−, B, and soluble Na+ in a clay loam soil. Irrigation water with an electrical conductivity of 1.5 dS m−1 was applied for four years. The greatest accumulation of soil salinity (electrical conductivity of the saturation soil extract, ec e) of 5.7 dS m−1 was beneath the trickle line for the 50% of et c treatment (14.0 m3 of applied water tree−1 yr−1). Soil salinity decreased with distance from the trickle line. Increasing the water volume to 100 and 150% of et c (26.9 and 40.3 m3 tree−1 yr−1, respectively) moves the zone of salt accumulation farther from the trickle line. The apparent leaching fraction based upon the Cl− ratio for the 50% of et c treatment was about 0.05 indicating loss of water by deep percolation within about 1 m of the trickle line. For trees irrigated at 100% of et c, the leaching fraction was 0.22 up to a distance of 1 m from the line, then decreased to 0.06 at a distance of 1.6 m. The leaching fraction for the 150% of et c treatment was from 0.36 within 1 m of the trickle line and then decreased to about 0.34 at 1.6 m from the line. Reasons for the leaching fraction being higher than expected are discussed. Further research is required to optimize the management of trickle irrigation to meet the et c and leaching requirements in young almond orchards irrigated with slightly saline water.